[Elecraft] Elecraft K3 drain at 5 watts CW only.

[Ariel Jacala]

For a K2 or K3, using 2 amps as a reasonable current drain on TX and 50% duty cycle.  Operating for a 24 hour period -   12h will be on TX.   A safe bet will be to have a 20Watt panel keeping a 30amp-hour SLA reasonably topped up for night time operation allowing for a 15 a-h drain maximum will get you 7.5h of TX time.  Better to have more and not need it than otherwise.  That will be my set-up for Field Day using a KX3.  Since the current drain on a KX3 is lower than that of a K2 or a KX3 on TX and RX,  approximately 1 amp on TX, I could probably get by without a solar panel with a 30 a-h SLA or use 15a-h with a panel.  For a K2 or K3 in QRP mode I would go the full 30 -h SLA and a panel.  In the above, overestimating the duty cycle approximates the receive duty since that was not explicitly calculated.

More accurately:
K2 or K3
Outflow = 12h(2 amps) + 12h(0.2 amps) =  26.4 a-h
Inflow = 12h*50%efficiency*1 amp = 6 amp-h
Net Outflow ~ 20 amp hr
Need 40 a-h battery with a 20w panel
So if the TX duty cycle is lower than 50% - you might be able to get by with a 30 a-h battery with a panel

KX3
Outflow = 12h(1 amps) + 12h(0.15 amps) =  13.8 a-h
Inflow = 12h*50%efficiency*1 amp = 6 a-h
Net Outflow ~ 7.8 a-h
Need 16 a-h with a panel or 30 a-h battery without a panel

Ariel NY4G

Sent from my iPad

On Jun 15, 2013, at 10:15 AM, "Philip Townsend Lontz" <philji at mac.com> wrote:

> 
> So, for Field Day running CW only any ideas about what the required amp hours will be?
> 
> Sent from my iPad
> 
> On Jun 15, 2013, at 8:06 AM, Michael Babineau <mbabineau at magma.ca> wrote:
> 
>> Robert : 
>> 
>> If you are planning to use Lead-Acid technology (SLA or wet-cell )
>> then, as others have suggested, you should double your calculated capacity, as you never want
>> to drain a Lead-Acid battery by more than 50% ..
>> 
>> so 
>> 
>> 10 hr requires 7 Ah
>> 20 hr requires 15 Ah 
>> etc.
>> 
>> The reality is that you will probably spend somewhat more than 50% of the time listening and tuning around
>> for stations when you are S&P so the real split may be more like 30% TX and 70% RX, but 50/50 is probably
>> a good guess. 
>> 
>> One further point .. don't discharge a Lead acid battery below 10.5 v. Repeatedly doing this will shorten
>> its lifespan.  Don's suggestion of setting the low voltage indication on the K2 to 11v is a good idea.
>> 
>> For picnic-table-portable operations, battery booster packs (intended to jump-start cars) work very well
>> and it is easy to find one with an SLA in the 10Ah to 20Ah range, often on sale. You can take the plastic
>> case apart to install some fusing and even powerpole connectors to customize it for your application
>> (I also removed the jumper cables from mine).  Some of these packs now even come with USB ports to allow for impromptu 
>> powering/charging of i-Devices.  It is often cheaper to buy one of these than to purchase just the equivalent capacity SLA
>> battery .. so you get a nice carrying case with a handle and other goodies for free. 
>> 
>> Best of luck ...
>> 
>> Michael VE3WMB 
>> 
>> 
>> 
>>> From: Robert G Strickland <rcrgs at verizon.net>
>>> Date: June 14, 2013 6:28:10 PM EDT
>>> To: Elecraft <elecraft at mailman.qth.net>
>>> Subject: [Elecraft] K2 qrp battery drain estimation
>> 
>> 
>>> If I'm operating a K2 at 5w cw, in S&P contest mode, I compute the current drain under the stated conditions as follows:
>> 
>>> conditions:
>>> 50% listening, 50% transmitting
>>> CW 50% duty cycle
>> 
>>> current:
>>> 200ma receive, more or less
>>> 1.0a transmit, more or less
>> 
>>> current draw per hour:
>>> 100ma [30min rcv] + 250ma [30min xmit @ 50% duty cycle] = 350ma per hour
>> 
>>> 10Hr requires a 3.5Ahr battery
>>> 20Hr requires a 7.5Ahr battery
>>> etc...
>> 
>>> Is this more or less accurate, or have I missed something? Thanks.
>> 
>>> ...robert
>> -- 
>>> Robert G Strickland, PhD ABPH - KE2WY
>>> rcrgs at verizon.net.usa
>>> Syracuse, New York, USA
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